<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        * {
            margin: 0;
            padding: 0;
        }

        .box {
            width: 1000px;
            height: 300px;
            margin: 100px auto;

        }

        .center {
            float: left;
            width: 400px;
            height: 300px;
            text-align: center;
            line-height: 300px;
            color: beige;
            background-color: brown;
        }

        .content {
            float: right;
            width: 300px;
            height: 300px;
            text-align: center;
            line-height: 300px;
            color: beige;
            background-color: chocolate;
        }

        .nav {
            float: left;
            width: 1000px;
            height: 100px;
            line-height: 100px;
            text-align: center;
            color: beige;
            background-color: deepskyblue;
        }
    </style>
</head>

<body>
    <div class="box">
        <div class="center">
            1
        </div>
        <div class="content">
            2
        </div>
        <div class="nav">
            3
        </div>
    </div>

</body>

</html>